As is well known a conductive enclosure shields the interior cavity defined by the enclosure from electromagnetic (EM) radiation. The conductive material forms a block to photons and the effectiveness of the block depends upon the thickness of the material, the frequency of the photon and the electromagnetic properties of the material (electrical conductivity and magnetic permeability). For metal at radio frequencies, thin layers can provide effective high impedance shields.
There is a current trend towards using metallic housings for electronic apparatuses. A metallic housing may be used for a number of reasons. It may, for example, provide a good electrical earth for the apparatus or it may, if applied as an exterior coat, where it provides a pleasing look and feel.
It is now becoming common for an electronic apparatus to include wireless RF technology. Such technology includes, for example, sensing technology such as RFID, mobile cellular technology such as UMTS, GSM etc, cable-less technology such as Bluetooth and wireless USB and networking technology such as WLAN.
It would be desirable to provide an apparatus that is functional in one or more of these wireless technologies and uses a conductive housing.
One solution would be to provide one of more external antennas for the apparatus but this is undesirable as it increases the size of the apparatus and also decreases it eye appeal.